Identity verification is useful in many applications. Examples include verifying identity prior to activating machinery or gaining entry to a secure area. Another example would be identity verification of an individual for matching that individual to records on file for that individual, such as for matching hospital patient records when the individual's identity is unknown. Identity verification is also useful to match police records at the time a suspect is apprehended, but true identity of the suspect is not known. Passwords, keys, numeric codes and fingerprints are solutions currently in use. However, keys and codes can be used by anyone having possession of the keys or codes. A requirement that the person physically at a site be the person authorized to use the key or password is not easily enforced. Fingerprint analysis generally fails to give instant results and security systems relying on fingerprint analysis can be circumvented, as disclosed by Osten et al. in U.S. Pat. No. 5,719,950.
Living human tissue is recognized as a dynamic system containing a multitude of components and analyte information that is particularly useful in the medical profession for diagnosing, treating and monitoring human physical conditions. To this end, effort has been directed toward developing methods for non-invasive measurement of tissue constituents using spectroscopy. The spectrographic analysis of living tissue has been focused on the identification of spectral information that defines individual analytes and relates such spectral data to the analyte's concentration. Concentrations of these analytes vary with time in an individual patient. Acquiring tissue spectral data with sufficient accuracy for use in diagnosis and treatment has proven difficult. Difficulties in conducting the analysis have been found which are related to the fact that the tissue system is a complex matrix of materials with differing refractive indices and absorption properties. Further, because the constituents of interest are many times present at very low concentrations, high concentration constituents, such as water, have had a detrimental impact on identifying the low level constituent spectral information and giving an accurate reading of the desired constituent concentration. Development of these techniques has always focused on the changes in spectral output with change in concentration of a dynamic analyte of interest, such as glucose. The techniques disclosed are focused on identifying concentrations of specific analytes, the concentration of which is expected to vary with time.
Improved methods and apparatus for gathering and analyzing a near-infrared tissue spectrun for an analyte concentration are disclosed in commonly assigned U.S. patent applications and issued patents. U.S. Pat. No. 5,655,530 and U.S. patent application Ser. No. 08/844,501, filed Apr. 18, 1997, entitled “Method for Non-invasive Blood Analyte Measurement with Improved Optical Interface” relate to near-infrared analysis of a tissue analyte concentration which varies with time, with a primary focus on glucose concentrations in diabetic individuals. The methods and apparatus include placing a refractive index-matching medium between a sensor and the skin to improve the accuracy and repeatability of testing. U.S. patent application Ser. No. 09/174,812, filed Oct. 19, 1998, entitled “Method for Non-Invasive Blood Analyte Measurement with Improved Optical Interface” discloses additional improvements in non-invasive living tissue analyte analysis. The disclosure of each of these three applications or patents are hereby incorporated by reference.
U.S. Pat. No. 5,636,633 relates, in part, to another aspect of accurate non-invasive measurement of an analyte concentration. The apparatus includes a device having transparent and reflective quadrants for separating diffuse reflected light from specular reflected light. Incident light projected into the skin results in specular and diffuse reflected light coming back from the skin. Specular reflected light has little or no useful information and is preferably removed prior to collection. U.S. patent application Ser. No. 08/871,366, filed Jun. 9, 1997, entitled “Improved Diffuse Reflectance Monitoring Apparatus”, discloses a further improvement for accurate analyte concentration analysis which includes a blocking blade device for separating diffuse reflected light from specular reflected light. The blade allows light from the deeper, inner dermis layer to be captured, rejecting light from the surface, epidermis layer, where the epidermis layer has much less analyte information than the inner dermis layer, and contributes noise. The blade traps specular reflections as well as diffuse reflections from the epidermis. The disclosures of the above patent and application, which are assigned to the assignee of the present application, are also incorporated herein by reference.
U.S. Pat. No. 5,435,309 relates to a system for selecting optimal wavelengths for multivariate spectral analysis. The use of only one wavelength gives insufficient information, especially for solutions having multiple components. The use of too many wavelengths can include too much noise and lead to combinatorial explosion in calculations. Therefore, the number of wavelengths used should be limited and the wavelengths well chosen. Genetic algorithms are used in this reference to select the most fit wavelengths. The disclosure of this patent is incorporated herein by reference.